WO2018210452A1 - Method for operating an electric grid - Google Patents

Abstract

The invention relates to a method for operating an electric grid that comprises a first sub-grid (42) and a second sub-grid (34) which are connected together via at least one DC-DC converter. The first sub-grid (42) has a multilevel converter (45) with a plurality of individual modules (48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d), and the first connection side of the at least one DC-DC converter is connected to the multilevel converter (45) via at least one double star point tap. The double star point tap is implemented via a first connection to a first star point of the multilevel converter and a second connection to a second star point of the multilevel converter, wherein at least one primary electric AC voltage is provided to the first sub-grid (42) by the multilevel converter (45), and at least one first electric DC voltage which is provided to the at least one DC-DC converter is tapped at the first connection side of the at least one DC-DC converter via the double star point tap and is transformed into an outgoing second electric DC voltage by the at least one DC-DC converter, said outgoing second electric DC voltage being provided to the second sub-grid (34).

Description

 Method for operating an electrical network

The invention relates to a method for operating an electrical network, a multilevel converter and a power supply system.

An electrical network can have a plurality of energy sources, via which a plurality of consumers, which are connected to the electrical network, electrical energy can be provided. In this case, it is furthermore possible for the electrical network to be subdivided into a number of subnetworks to which different energy sources and consumers are assigned. The different subnetworks may have different voltages with which the subnetworks are to be operated, these different voltages having different amplitudes and / or different maximum values. Two interconnected subnets with different ones

Voltages are connected to one another via a voltage converter, for example a DC-DC converter or an AC-DC converter.

From the document US 5 093 583 A an electrical system for a motor vehicle is known which comprises a low-voltage network and a high-voltage network. In this case, a low-voltage voltage is generated by a generator that the

Low-voltage network and a transformer of the motor vehicle feeds. This transformer is designed to convert the low-voltage into a high-voltage, with the consumers of the high-voltage network to operate parallel to consumers of the low-voltage network. A method for supplying an electric motor with an alternating current is described in US 2010 0 140 003 A1. In this case, depending on the requirements of the electric motor, it is provided with an electrical voltage via at least one pulse width modulation, whereby a plurality of types, for example three types, of a respective pulse width modulation to be used are selected. From the document US 2013 0 106 365 AI is known to charge an energy storage of an electric motor vehicle via an external power source. It is possible, the energy storage of the motor vehicle with the external power source galvanically isolated or directly charged.

A fuel cell system, via which electrical loads are to be supplied with electrical energy, is described in the publication US 2014 0 152 089 AI. Here, between each one fuel cell and each of an electrical load

Inverter disposed which is adapted to generate a multi-phase high voltage required by the respective load, wherein disturbing noises are avoided by selecting a difference of phases of the high-voltage voltages.

From document US 2014 0 225 432 AI a current transformer is known which comprises three coils and is designed to exchange electrical energy between different voltage sources and voltage networks of an electric motor vehicle.

Against this background, it was an object of the present invention to provide a method and a device with the voltages or with

different maximum values are to be generated, wherein a first consumer, which is to provide a first voltage with a first value, by a second

Voltage with a second value, which is to provide a second consumer is not disturbed. This object is achieved with the method according to claim 1, a

Multilevel converter according to the independent claim 8 and a

Energy supply system according to independent claim 16 solved.

Embodiments of the method, the multilevel converter and the

Power supply system result from the dependent claims and the description. The method according to the invention is intended for operating an electrical network, which comprises a first subnetwork and a second subnetwork, which are connected to one another via at least one DC-DC converter. In this case, a first connection side of the at least one DC-DC converter is assigned to the first sub-network and a second connection side of the at least one DC-DC converter to the second sub-network. The first subnetwork has a multilevel converter with a plurality of individual modules, wherein each individual module has an electrical energy store, wherein the first connection side of the at least one

DC converter is connected via at least one double neutral point tap to the multilevel converter. The double star point tap is implemented via a first connection to a first neutral point of the multilevel converter and a second connection to a second neutral point of the multilevel converter. The multilevel converter provides at least one primary alternating electrical voltage to the first subnetwork. On the first connection side of the at least one DC-DC converter, at least one first DC electrical voltage is tapped via the double neutral point tap, which is the at least one

DC converter is provided, and of the at least one

DC converter is transformed to an outgoing second DC electrical power, which is provided to the second subnet.

In a possible embodiment, the DC-DC converter comprises a transformer which galvanically separates the first sub-network and the second sub-network, a primary side of the transformer having a first number of turns being assigned to the first sub-network and a secondary side of the transformer having a second number of turns being assigned to the second sub-network. The transformer is preceded by an inverter on the primary side, which converts the tapped via the double neutral point tap at least a first DC voltage in a first AC voltage, the

Transformer is provided, is transformed by this into a second AC voltage and from a transformer on the secondary side

downstream rectifier is transferred to the outgoing second electrical DC voltage. Usually, the first number of turns of the primary side of the transformer is greater than the second number of turns of the secondary side. In the method, it is provided that the first alternating voltage has an amplitude with a first value and a frequency with a first value, and that the second alternating voltage has an amplitude with a second value and a frequency with a second value. In this case, the first value of the amplitude of the first alternating voltage is usually set greater than the second value of the amplitude of the second alternating voltage. The first value of the frequency of the first alternating voltage is usually smaller than the second value of the frequency of the second

AC voltage set. Alternatively, it is possible that the first value of the amplitude of the first alternating voltage is smaller than the second value of the second alternating voltage. It is also possible that the value of the frequency of the first

AC voltage is greater than the value of the frequency of the second AC voltage.

In an alternative embodiment, the Gleichspannungswandller with a

Transducer topology realized without galvanic isolation. It is conceivable that a converter from the group consisting of: buck converter, boost converter, buck-boost converter, boost-buck converter is selected as a DC-DC converter.

In a further embodiment, via the double star point tap a respective direct or indirect tap on the electrical energy storage of the respective to the first star point and the second star point of

Multilevel converter nearest individual modules of the multilevel converter

performed. These individual modules, from which or from their energy stores the at least one first DC voltage is tapped, are referred to below as star point modules. In a further embodiment of the method according to the invention are of the

Multilevel converter the first subnet several, for example, three, to each other

phase-shifted primary AC voltages or phases provided. The multi-level converter comprising a plurality of individual modules with energy stores is designed and / or designated as an energy store or energy source, with the consumers of the subnets being provided with different voltages. Here are consumers of the first sub-network AC voltages with each

according to needs adjusted amplitudes and frequencies provided.

Furthermore, consumers of the second subnet are provided via the DC-DC converter an outgoing second DC voltage whose size is set to a demand demanded by consumers of the second subnetwork. In an embodiment, the DC-DC converter, as explained above, comprises a transformer, wherein the primary side of which is assigned to the first subnet and whose secondary side is assigned to the second subnet. The transformer is on its primary side

Inverters upstream of which the first of the so-called

Star point modules, i. is taken from the respective nearest the two star points nearest individual modules tapped DC voltage in the first AC voltage. The first AC voltage is transferred from the transformer to a second one

Transformed alternating voltage, wherein the frequency and the amplitude of which depends on the frequency and amplitude of the first alternating voltage and on a ratio of the two numbers of turns of the transformer. In addition, the multilevel converter has a plurality of distributed individual modules, wherein a DC voltage or an AC voltage is provided by an energy store of a respective individual module, wherein in the event that a DC voltage is provided by a respective energy store, this DC voltage is converted by the multilevel converter into an AC voltage. The multilevel converter or multistage converter according to the invention, which may also be referred to as multilevel converter, is to be arranged in an electrical network which comprises a first subnetwork and a second subnetwork, wherein the two subnetworks are to be connected to one another via at least one DC-DC converter. A first connection side of the at least one DC-DC converter is the first subnet and a second terminal side of the at least one DC-DC converter is assigned to the second subnet or assigned. The multilevel converter is to be arranged in the first subnetwork. The multilevel converter has a plurality of individual modules, wherein each individual module has an electrical energy store, wherein the multilevel converter is configured to provide the first subnet at least one primary AC voltage and a double star point tap on the first terminal side of the at least one DC-DC converter

DC converter to provide at least a first DC voltage to be transformed by the at least one DC-DC converter to an outgoing second DC electrical voltage and the second subnet is to provide. The double star point tap is via a first connection to a first

Starpoint of the multilevel converter and a second connection to a second neutral point of the multilevel converter to realize or realized. In a possible embodiment of the DC-DC converter is fully or at least partially integrated into the multilevel converter, d. H. All or some components of the DC-DC converter are also components of the multilevel converter.

The multilevel converter is assigned a control unit which is designed to set values of at least one physical parameter, for example an amplitude and / or a frequency, of the at least one primary AC voltage and / or the first DC voltage. Depending on the definition, this control unit is designed and / or designated as a component of the multilevel converter. Furthermore, at least two individual modules of the multilevel converter, usually all individual modules, are the same. The multilevel converter is designed to supply the at least one primary AC voltage from a single voltage from an energy source or a

Generate or provide energy storage at least one single module, wherein a plurality of primary alternating voltages superimposed on each other and / or phase-shifted in time.

In addition, the multilevel converter is designed to switch at least two individual modules in series and / or parallel to one another, and the at least one primary

To provide AC voltage from a combination of individual voltages of the at least two individual modules to be combined. In this case, individual individual modules are switched on or off as required.

The multilevel converter has a plurality of, for example, three strands, wherein each strand has a combination of a plurality of interconnected, usually identically designed individual modules, wherein a primary alternating voltage and thus phase is to be generated with each strand. The value of the amplitude of the respective primary alternating voltage is set depending on which individual module of a respective strand is switched on or off and how several switched individual modules of the strand are connected to each other in series and / or in parallel.

The energy storage of the individual modules are usually designed as DC voltage sources. The multilevel converter has at least one converter which is designed to generate a single voltage of a DC voltage

Convert energy storage of at least one single module into an AC voltage and to provide the at least one primary AC voltage.

In this case, via the double star point tap a respective direct or indirect tap on the electrical energy storage of the respective nearest to the first neutral point and the second neutral point of the Multilevelkonverters Single modules of the multilevel converter, ie of the star point modules of the

Make multilevel converter.

In an embodiment, the DC-DC converter is an integral part of

Multilevel converter.

In refinement, the DC-DC converter comprises a transformer whose primary side is assigned to the first subnet and whose secondary side is assigned to the second subnet. On the primary side, the transformer is an inverter or

Inverter upstream, which is designed to convert the tapped from the star point modules or tapped first DC voltage into a first AC voltage and provide the primary side of the transformer.

This means that the primary side of the transformer through the first

AC voltage, d. H. by the inverter provided by the inverter

AC voltage, is excited.

The transformer has a high-pass characteristic, wherein by the

Transformer from the first AC voltage only shares taken into account and transformed to the second AC voltage, which is at least as large as a

Limit frequency are.

The energy supply system according to the invention comprises an electrical network comprising a first subnetwork and a second subnetwork, which has at least one

DC-DC converter are connected together. In this case, a first connection side of the at least one DC-DC converter is assigned to the first sub-network and a second connection side of the at least one DC-DC converter to the second subnet, the first subnet having a multilevel converter with a plurality of individual modules, each individual module having an electrical energy store. The first terminal side of the at least one DC-DC converter is at least a double star point tap to the multilevel converter connected, wherein the double star point tap is realized via a first connection to a first neutral point of the multilevel converter and a second connection to a second neutral point of the multilevel converter. The IVIultilevelkonverter is adapted to provide at least one primary AC electrical voltage to the first subnetwork, and at the first terminal side of the at least one

DC converter via the double star point tap the at least one DC-DC converter at least a first DC electrical voltage

provide. The at least one DC-DC converter is adapted to the at least one first DC voltage to an outgoing second electrical

DC voltage to transform and provide the second subnet.

In one embodiment of the energy supply system according to the invention, the DC-DC converter comprises a transformer which galvanically separates the first sub-network and the second sub-network, wherein a primary side of the transformer with a first number of turns of the first subnet and a secondary side of

 Transformer with a second number of turns is assigned to the second subnet. In this case, the transformer is preceded by an inverter on the primary side, which is designed to convert the at least a first DC voltage to be taken over the double star point tap into a first AC voltage and the

To provide transformer. The transformer is configured to transform the first AC voltage provided by the inverter into a second AC voltage, wherein the transformer on the secondary side, at least one rectifier is connected downstream, which is adapted to provide the second AC voltage provided by the transformer in the outgoing second electrical

To convert DC voltage.

In an embodiment, the first number of turns of a coil of the primary side of

Transformer greater than the second number of turns of a coil of the secondary side of the transformer. Alternatively, it is conceivable that the first number of turns of the coil of the primary side is smaller than the second number of turns of the coil of the secondary side. According to a further embodiment, the

 Gleichspannungswandller a converter topology without galvanic isolation on.

It is conceivable that the DC-DC converter is a converter from the group consisting of: buck converter, boost converter, buck-boost converter, boost-buck converter.

In one embodiment of the energy supply system according to the invention, the double star point tap is over a respective immediate or indirect

Connecting the first neutral point and the second neutral point to the electrical energy storage of the respective to the first neutral point and the second

Star point of the multilevel converter nearest individual modules of the

Multilevel converter, i. to realize from the star point modules. The energy supply system is, for example, to be arranged in a motor vehicle.

Furthermore, the first subnet is to be assigned as consumer an electrical machine which has a plurality of phases, wherein the multilevel converter is designed to provide a primary alternating voltage for each phase.

The presented multilevel converter according to the invention is in an embodiment as

Component of the proposed power supply system according to the invention, wherein the multilevel converter and / or the

Energy supply system consumers of the network, ie at least one consumer of the first subnet, which is usually designed as an electrical machine, and at least one consumer of the second subnet to be supplied with electrical energy. In an embodiment, it is provided that such an electrical machine is operated as an electric motor with which electrical energy is converted into mechanical energy. Alternatively or additionally, it is also possible that this electrical machine is operated as an electric generator depending on the requirement. If the energy supply system and the network are provided for a motor vehicle, the network is also designed as an on-board network of the motor vehicle. Correspondingly, the two subnetworks are designed and / or designated as partial subsystems of the motor vehicle which are to be operated with voltages whose amplitudes or maximum values are of different sizes. In this case, it is further provided that the electrical machine is designed as a consumer of the first subnetwork whose voltage has an amplitude of a large value, if it is operated as an electric motor, for driving or moving the motor vehicle. If the electric machine is alternatively operated as an electrical generator, this mechanical energy of the motor vehicle, for example. In a recuperation, to convert into electrical energy, while providing electrical energy to be stored in an energy storage of the electrical network. A consumer of the second subnetwork, whose voltage is usually lower, is, for example. For

Carrying out a control function of the motor vehicle trained.

The proposed method according to the invention is to be carried out with the multilevel converter and / or the power supply system, the method having the

Multilevel converter and / or the power supply system to control and thus to control and / or to regulate.

In an embodiment, the multilevel converter is designed as a high-voltage multilevel converter if the first subnetwork is to be operated with a higher voltage than the at least one second subnetwork. The value of the frequency of the at least one primary alternating voltage, which is provided by the multilevel converter and with which the load of the first subnetwork is to be supplied, is generally comparatively low and amounts to a maximum of two kilohertz.

The multilevel converter is designed, for example, as a modular multilevel converter (MMC) or MMSPC. One trained as MMSPC

Multilevel converter is in the publication "Modular Multilevel Converter with Series and Parallel Module Connectivity: Topology and Control. "(IEEE Transaction on Power

Electronics) by S.M. Goetz, A.V. Peterchev and T. Weyh.

As a rule, the at least one primary alternating voltage to be generated has a high degree of dynamics. Usually, the value of the amplitude of the at least one primary AC voltage is in the size range of> 200V. By combining a plurality of primary alternating voltages, which are superimposed by the multilevel converter, so-called frequency multiplexing of the primary alternating voltages is possible, whereby the primary alternating voltages thus combined are to be supplied to supply the load of the first subnetwork starting from the multilevel converter. The amplitude and / or frequency of the primary alternating voltages are adapted to requirements of the consumer of the first subnetwork.

A high-pass characteristic of the transformer provided in the embodiment is to be set by selecting a value of an inductance of at least one of the two coils or of the transformer, wherein the inductance of the respective coil is dependent on its number of turns.

The excitation of the transformer is set by the value of the frequency and / or the amplitude of the first AC voltage provided by the multilevel converter via the inverter upstream of the transformer.

The secondary side of the transformer provided in the embodiment is then provided with at least one rectifier and thus possibly a topology of several

Rectifiers connected to the at least one rectifier turn at least one load of the second subnet is connected, wherein the output of the transformer provided by the second alternating voltage is converted by the at least one rectifier into the second DC voltage. The at least one rectifier is usually active or passive and generally has at least one DC control stage, which is embodied, for example, as a Buck, Boost, or Buck Boost stage. Furthermore, the rectifier can be followed by an inverter to realize an output of 110V or 240V. The topology formed by the at least one rectifier is at least one pulse or multi-pulse, for example one-pulse to twelve-pulse. To actively control the at least one

Rectifier is, for example, to use as a field effect transistor (FET) formed semiconductor device. For passive rules, for example, at least one diode is to be used.

In a first possible embodiment of the method, of the multilevel converter and / or of the energy supply system, it is provided that the first subnetwork as the high-voltage power supply network and the second subnetwork as

Low-voltage power supply network is formed. In this case, the second subnetwork in design has at least one own energy store, for example a capacitor and / or a battery. An average power requirement of the first subnetwork is a multiple, for example a factor of five, higher than the average power requirement of the second subnetwork. If the power supply system and thus the electrical network for a motor vehicle is used, the average power requirement of the second subnetwork with a maximum voltage of, for example, 12V, 24V, 48V, 400V, 800V is 1 to 3 kW. By contrast, the power requirement of the first subnetwork, depending on the configuration of the motor vehicle to be driven for its drive, for example, 20 kW to 400 kW.

In the inventively provided or to be performed double

Star point tap of the first DC voltage from the Mulitlevelkonverter or from its neutral point modules power is removed from the first subnet. In order for a current power of the first subnetwork, which results from an actual nominal current or desired voltage profile based on the at least one primary AC voltage, to follow a current control setpoint, the first DC voltage to be tapped or tapped is via a dynamic power control of the first subnetwork essentially to compensate. By using the degrees of freedom of the multilevel converter as a physical circuit, the voltage tap becomes relative to reference points of the multilevel converter carried out. These reference points correspond to respective star points of the multiphase multilevel converter or multilevel converter. The tap of the at least one first DC voltage is in this case between each

Connections of the star point modules carried out at the two star points. The DC voltage tap is connected in parallel to connections of all star point modules of the

Multilevel converter, i. performed at all stages, with a uniform

Load distribution takes place on all strands of the multilevel converter.

With the presented multilevel converter or multilevel converter is to provide a primary AC voltage, which has a low distortion, which disturbances of other electrical devices are avoided. Within the first

Subnetwork, electrical energy provided by the multilevel converter is used by the electric machine to drive the motor vehicle. It is possible, the electric machine starting from the multilevel converter

to operate voltage-controlled.

The multilevel converter is, for example, as a neutral-point-clamped (NPC) converter, which has a neutral at a neutral point, as a flying capacitor, as a modular

Multilevel converter or designed as MMSPC, with each of which, for example, alternating or three-phase voltages for at least one electric machine for driving a motor vehicle can be provided. Such provided for supply voltage has a value in the high-voltage range greater than 60 volts, usually greater than 200 volts and is usually from several energy storage, eg. High-voltage storage, fed. At least one output of the multilevel converter is galvanically isolated from the at least one high-voltage storage. If the multilevel converter has several outputs, these are also galvanically isolated from each other.

About the first subnetwork, which has the multilevel converter is the electrical

To provide power to the machine, wherein the first subnet is designed and / or designated as a high voltage system. In contrast, the second subnet is called

Low-voltage system formed and / or to designate the other Consumers, eg. Lighting equipment, ancillaries, control or

Control modules or communication devices of the motor vehicle to be supplied with electrical energy. The second subnetwork has, for example, a maximum voltage of 12 V, 24 V, 48 V, 400 V, 800 V. In contrast, the first subnet has voltages of, for example, 110 V or 240 V.

In a possible embodiment, the subnets are galvanically isolated from each other via the transformer, so that a possible semiconductor damage in the first subnet can not produce a conductive connection to the second subnet and thus, for example, no life-threatening touch voltage. The multilevel converter used to provide the electrical energy has a low weight and requires only a small space. The multilevel converter can be used to implement a galvanically isolated converter function with at least one inverter. The modular multilevel converter, for example, is embodied as an M2SPC (modular multilevel parallel-serial converter) and comprises capacitors and / or batteries as multiple energy stores or components of the individual modules of the multilevel converter.

The multilevel converter, which comprises several individual modules, is considered to be more central

Energy storage of the power supply system used, with the

Multilevel converter within the first subnet to generate a high voltage. Starting from the DC voltage tap to star point modules of the

Multilevel converter is provided with the DC-DC converter for the second subnet a comparatively low voltage, these two subnets are separated from each other via the DC-DC converter. The one of the

Multilevel converter provided voltage is subject to only slight fluctuations. With the multilevel converter several batteries can be dynamically reconfigured as energy storage and thus also be used for a motor vehicle.

In an embodiment, with the usually modular Multilevelkonverter of several energy storage devices of the individual modules, which are formed, for example, as a DC voltage sources, the AC voltage for the first subnetwork, the high value of the voltage has generated. In the proposed power supply system, the second subnet is connected via the DC-DC converter to the first subnet, wherein an energy exchange is made possible between the two subnetworks. The transformer provided as part of the DC-DC converter is supplied with electrical energy with the usually small first first AC voltage provided by the upstream inverter. This first AC voltage is generated via the first DC voltage, wherein it is possible via the provided double star point tap that the tapped first DC voltage substantially does not affect an operation of the electrical machine.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is schematically illustrated by means of embodiments in the drawings and will be described schematically and in detail with reference to the drawings. FIG. 1 shows a schematic representation of a first embodiment of the invention

inventive multilevel converter.

FIG. 2 shows a schematic representation of a first embodiment of the invention

Energy supply system according to the invention. FIG. 3 shows a schematic representation of a second embodiment of the energy supply system according to the invention.

The figures are described coherently and comprehensively. equal

 5 components are assigned the same reference numbers.

The first embodiment of the multilevel converter 10 according to the invention shown schematically in FIG. 1 comprises a first strand 12 with four individual modules 14a, 14b, 14c, 14d, a second strand 16 with likewise four individual modules 18a, 18b, 18c, 18d

10 and a third strand 20 with four individual modules 22a, 22b, 22c, 22d. It is possible to designate each of said strands 12, 16, 20 as the arm of the multilevel converter 10. This modular multilevel converter is designed, for example, as an MMC, MMSPC or Matroschka converter, which is described in the German patent application DE 10 2015 112 513. Each of the individual modules 14a, 14b, 14c, 14d, 18a, 18b,

15 18c, 18d, 22a, 22b, 22c, 22d comprises at least one energy store, for example a capacitor or a battery, for which reason the multilevel converter 10 has a plurality of distributed energy stores. With energy storage of the individual modules 14a, 14b, 14c, 14d of the first strand, energy is to be provided here to a first phase of an electrical machine. A second phase of this electric machine is about the

 20 individual modules 18a, 18b, 18c, 18d of the second strand 16 electrical energy

 provide. In addition, with the individual modules 22a, 22b, 22c, 22d, of the third strand 20 of a third phase of the electrical machine to provide energy.

The schematically illustrated in Figure 2 first embodiment of the

The first subnetwork 42 comprises a second embodiment of the multilevel converter 45 according to the invention, which in turn has three strands 47, 49, 51 or arms connected in parallel to each other, a first such strand 47 a first single module 48a, a second single module 48b, a third single module 48c and a fourth one

30 individual module 48d has. A second strand 49 of the multilevel converter 45 has a first individual module 50a, a second individual module 50b, a third individual module 50c and a fourth individual module 50d on. In addition, the multilevel converter 45 comprises a third strand 51 having a first individual module 52a, a second individual module 52b, a third individual module 52c and a fourth individual module 52d. In this case, all the individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d each have an energy store designed as a battery or as a capacitor.

In each case one strand 47, 49, 51 of the multilevel converter 42 is assigned to a phase of a total of three phases U, V, W of an electrical load 58, which is embodied here as an electrical machine 10.

During operation of the multilevel converter 45, a value of an amplitude of a primary alternating voltage, that of a respective phase U, V, W of the consumer 58

 is to be provided via the control unit 54. Here, a first phase U 15 of the first strand 47 with the individual modules 48a, 48b, 48c, 48d assigned. one

 second phase V of the consumer 58, the second strand 49 is associated with the individual modules 50a, 50b, 50c, 50d. In addition, the third phase W of the load 58 of the third strand 51 is associated with the individual modules 52a, 52b, 52c, 52d.

20 All individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d are of similar design and each have a similar energy storage, with each of which an alternating voltage is to provide whose amplitude has the same value , Depending on what value the amplitude of the AC voltage should have, which is to provide a respective phase U, V, W, is or be of the

25 control unit 54 within a respective strand 47, 49, 51 at least one

 Single module 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d, generally a plurality of individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d activated, whereby, depending on the value of the amplitude of the alternating voltage to be provided, for example at least two individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a,

30 52b, 52c, 52d within a respective strand 47, 49, 51 to each other in series

and / or in parallel. Here, it is generally provided that the first subnet 42 is operated with a voltage which is higher than a second voltage of the second subnet 34. Both subnetworks 42, 34 are connected to each other here via a galvanically isolating transformer 60, wherein the primary side of the transformer 60 is assigned to the first subnetwork 42 and a secondary side of the transformer 60 to the second subnetwork 34. In addition, the transformer 60 is connected downstream of a rectifier 62 within the second subnetwork 34, to which an energy store 64 is connected. Furthermore, a first neutral point 66 and a second neutral point 67 are defined for the multilevel converter 45. Each of the three strands 47, 49, 51 is above each one

Single module, strand 47 via individual module 48a, strand 49 via individual module 50a and strand 51 via individual module 52a, connected to star points 66 and 67. Each of these individual modules 48a, 50a and 52a is connected via its respective energy store indirectly or directly to both the star point 66 and the neutral point 67, so that when performing an embodiment of the

inventive method of the individual modules 48a, 50a, 52a, which are also referred to as star point modules, a first DC voltage is tapped. The thus tapped first DC voltage is then fed to an inverter 55, which converts the first DC voltage into a first AC voltage and the

Transformer 60 provides. The primary side of the transformer 60 is connected to the inverter 55. The secondary side of the transformer 60 is connected to the downstream rectifier 62. The transformer 60 transforms the first AC voltage into a second AC voltage, which is converted via the downstream rectifier 62 into a second DC voltage. The second DC voltage is provided to the second subsystem 34 and supplied to the energy storage 64 here.

The series connection of inverter 55, transformer 60 and rectifier 62 shown here implements a DC-DC converter which electrically separates the first sub-network 42 and the second sub-network 34. The galvanic isolation is ensured here by the transformer 60. The galvanic isolation ensures that a possible semiconductor damage in the first sub-network 42 can not produce a conductive connection to the second sub-network 34 and thus, for example, no perilous touch voltage. In carrying out an embodiment of the method according to the invention, a three-phase system is provided with the individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d, of the respective strand 47, 49, 51.

Here, the first strand 47 of a first phase U, the second strand 49 of a second phase V and the third strand 51 of a third phase W of the consumer 58 is assigned. In the method, a respective potential of the star points 66, 67 is not clearly defined, but adjusted to a respective midpoint voltage of the three phases U, V, W. With the multilevel converter 45, which is designed here as a three-phase MMSPC, via the transformer 60 is an integrated galvanically isolated supply of

Consumers of the second subnet 34 allows.

The second embodiment of the energy supply system 70 according to the invention, shown schematically in FIG. 3, comprises a first subnetwork 72 and a second subnetwork 74. The first subnetwork 72 comprises a third embodiment of the multilevel converter 75 according to the invention. It is provided that the third embodiment of the multilevel converter 75 is largely identical in construction to The second embodiment of the multilevel converter 45 is formed.

Again, a value of an amplitude of a primary AC voltage for a respective phase U, V, W of the load 58 by a series and / or

Parallel connection of the individual modules 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d of each strand 47, 49, 51 is provided. The second embodiment of the power supply system 70 differs from the first embodiment of Figure 2 in that a located between the first subnet 72 and the second subnet 74 DC-DC converter 65 is not realized by a series connection of inverter, transformer and rectifier, but here as a DC-DC converter 65 is carried out without galvanic isolation. Here, one of the two star points 66, 67, here star point 66 is grounded directly, while the other star point, here star point 67, is connected to an energy store in the form of an inductor or coil 61. Connected downstream of the coil 61 are two transistors 63a, 63b which are in turn connected in series with one another and which are each designed here as a MOSFET. In turn, a DC-DC converter 65 is realized via the circuit of coil 61 and MOSFETs 63a, 63b. The MOSFETs 63a and 63b are here connected in series with each other, wherein the two MOSFETs 63a, 63b are each regulated at least against the potential of neutral point 66. The source terminals of the MOSFETs 63a and 63b face each other. The drain terminal of the MOSFET 63a is connected to the coil 61, and the drain of the MOSFET 63b is connected to the positive terminal of the energy storage 64.

When carrying out an embodiment of the method according to the invention is a via the two star points 66, 67 of the respective energy storage of

Star point modules 48a, 50a, 52a tapped first DC voltage across the coil 61 and the two MOSFETs 63a, 63b converted into a second DC voltage, which is the second sub-network 74 is provided.

In this second embodiment of the inventively provided

DC-DC converter is compared to the first shown in Figure 2

Embodiment to achieve higher efficiency, combined with a smaller space requirement and lower costs.

Claims

claims A method of operating an electrical network comprising a first subnetwork (42, 72) and a second subnetwork (34, 74) over at least one of  5 DC-DC converter are connected to each other, wherein a first  Connection side of the at least one DC-DC converter to the first subnetwork (42, 72) and a second terminal side of the at least one DC-DC converter is assigned to the second subnetwork (34, 74), wherein the first subnetwork (42, 72) with a multilevel converter (45, 75) Plurality of individual modules (14a, 14b, 14c, 14d, 10 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d), each individual module having an electrical module  Energy store, wherein the first terminal side of the at least one  DC converter is connected via at least one double neutral point tap to the multilevel converter (45, 75), wherein the double star point tap 15 is realized via a first connection to a first neutral point of the multilevel converter and a second connection to a second neutral point of the multilevel converter, wherein at least one primary electrical alternating voltage is provided by the multilevel converter (45, 75) to the first subnetwork (42, 72), and at the first terminal side of the at least one DC-DC converter over the double 20 star point tap at least a first DC electrical voltage is tapped, which is provided to the at least one DC-DC converter, and is transformed by the at least one DC-DC converter to an outgoing second DC electrical power, which is the second subnet (34, 74) is provided. 2. The method of claim 1, wherein it is provided that the  DC-DC converter comprises a transformer (60), which galvanically separates the first sub-network (42) and the second sub-network (34), wherein a primary side of the transformer (60) with a first number of turns of the first sub-network (42) and a secondary side of the transformer ( 60) with a second number of turns the second 30 subnet (34) is assigned, wherein the transformer (60) on the primary side of an inverter (55) is connected upstream of the tapped over the double neutral point tap converted at least a first DC voltage into a first AC voltage, which is the transformer (60) is transformed by the latter into a second AC voltage and from a transformer (60) on the secondary side downstream rectifier (62) transferred to the outgoing second DC electrical voltage becomes. 3. The method of claim 2, wherein the first AC voltage has an amplitude with a first value and a frequency with a first value, and that the second AC voltage has an amplitude with a second value and a frequency with a second value, wherein the first Value of the amplitude of the first AC voltage greater than the second value of the amplitude of the second AC voltage is set, and wherein the first value of the frequency of the first AC voltage is less than the second value of the frequency of the second AC voltage is set. 4. The method of claim 1, wherein the DC-DC converter is realized with a converter topology without galvanic isolation. 5. The method of claim 4, wherein as a DC-DC converter, a converter from the group consisting of: Buck converter, boost converter, buck-boost converter, Boost Buck converter is selected. 6. The method according to any one of the preceding claims, wherein the double star point tap a respective direct or indirect tap on the electrical energy storage of the respective to the first star point (66, 67) and the second star point (66, 67) of the Multilevelkonverters (45 , 75) nearest individual modules (48a, 50a, 52a) of the multilevel converter. 7. The method according to any one of the preceding claims, wherein of the Multilevel converter (45, 75) the first subnet (42, 72) more to each other phase-shifted primary AC voltages are provided. 8. IVIultilevelkonverter to be arranged in an electrical network, wherein the electrical network comprises a first sub-network (42, 72) and a second sub-network (34, 74), wherein the two sub-networks via at least one DC-DC converter with each other 5, wherein a first terminal side of the at least one  DC converter to the first subnetwork (42, 72) and a second terminal side of the at least one DC-DC converter assigned to the second subnetwork (34, 74), wherein the IVIultilevelkonverter is to be arranged in the first subnet and a plurality of individual modules (14a, 14b, 14c, 14d, 18a, 18b, 10 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d), each individual module having an electrical energy store, wherein the IVIultilevelkonverter (45, 75) is adapted to provide the first subnetwork (42, 72) at least one primary AC voltage and via a double star point tap on the first terminal side of the at least one  15 DC-DC converter the DC-DC converter at least a first  DC voltage to be transformed by the at least one DC-DC converter to an outgoing second DC electrical voltage and the second subnet (34, 74) is provided, the double star point tap via a first connection to a first neutral point (66, 67) of the multilevel converter ( 45, 20 75) and a second connection to a second star point (66, 67) of the  Multilevel converter (45, 75) can be realized. 9. IVIultilevelkonverter according to claim 8, which is associated with a control unit (54) which is adapted to values of at least one physical parameter of 25 at least one of the IVIultilevelkonverter the first subnet (42, 72)  to be provided primary AC voltage and / or the at least first  Set DC voltage. 10. IVIultilevelkonverter according to claim 8 or 9, wherein at least two individual modules 30 (14a, 14b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d) are identical. 11. Multilevel converter according to one of claims 8 to 10, which is adapted to the at least one the first subnet (42, 72) to be provided AC voltage from a single voltage from an energy storage at least one single module (14a, 5b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d). 12. Multilevel converter according to claim 11, which is designed to have at least two individual modules (14a, 14b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 10 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d) in series and / or to each other  in parallel, and the at least one of the first subnetwork (42, 72)  to be provided alternating voltage from a combination of individual voltages of at least two individual modules to be combined (14a, 14b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b , 50c, 50d, 52a, 15 52b, 52c, 52d). 13. Multilevel converter according to one of claims 8 to 12, which has a plurality of strands (12, 16, 20, 47, 49, 51), wherein each strand (12, 16, 20, 47, 49, 51) a  Combination of several interconnected individual modules (14a, 14b, 14c, 20 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d), with each strand ( 12, 16, 20, 47, 49, 51) in each case to generate a primary AC voltage to be provided to the first subnetwork (42, 72) or to be able to be generated. 25 14. Multilevel converter according to one of claims 8 to 13,  in which the respective energy stores of the individual modules (14a, 14b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 52a, 52b, 52c, 52d) are formed as DC voltage sources, wherein the double star point tap a respective direct or indirect tap on the electrical 30 energy stores from the respective to the first neutral point (66, 67) and the second Star point (66, 67) of the Multilevelkonverters (45, 75) closest individual modules (48a, 50a, 52a) of the Multilevelkonverters is made. 15. Multilevel converter according to claim 14, in which the DC-DC converter 5 is an integrative part of the multilevel converter (45, 75). 16. A power supply system comprising an electrical network comprising a first subnetwork (42, 72) and a second subnetwork (34, 74) connected to each other via at least one DC-DC converter, wherein a first terminal side 10 of the at least one DC-DC converter to the first sub-network (42, 72) and a second terminal side of the at least one DC-DC converter to the second subnet (34, 74) is assigned, wherein the first subnet (42, 72) a  Multilevel converters (45, 75) having a plurality of individual modules (14a, 14b, 14c, 14d, 18a, 18b, 18c, 18d, 22a, 22b, 22c, 22d, 48a, 48b, 48c, 48d, 50a, 50b, 50c, 50d, 15 52a, 52b, 52c, 52d), each individual module having an electrical  Energy store, wherein the first terminal side of the at least one  DC converter is connected via at least a double star point tap to the multilevel converter (45, 75), wherein the double star point tap via a first connection to a first neutral point (66, 67) of the multilevel converter 20 (45, 75) and a second connection to a second star point (66, 67) of the  Multilevel converter (45, 75) is realized, wherein the Multilevelkonverter (45, 75) is adapted to provide at least one electrical primary AC voltage to the first subnet (42, 72), and at the first terminal side of the at least one DC-DC converter via the double star point tap the at least one 25 DC-DC converter at least a first DC electrical voltage  wherein the at least one DC-DC converter is designed to transform the at least one first DC voltage to an outgoing second DC electrical voltage and to provide it to the second sub-network (34, 74). 17. Energy supply system according to claim 16, wherein the DC-DC converter comprises a transformer (60) comprising the first sub-network (42) and galvanically isolating the second subnet (34), wherein a primary side of the first turn number transformer (60) is associated with the first subnet (42) and a secondary side of the second winding transformer (60) is associated with the second subnet (34); wherein the transformer (60) on the primary side 5 inverter (55) is arranged, which is designed to be over the double  The transformer (60) is adapted to transform the first AC voltage provided by the inverter (55) into a second AC voltage, wherein the transformer (60) is designed to transform the at least one first DC voltage to be taken off star point tap into a first AC voltage 10 transformer (60) on the secondary side at least one rectifier (62)  connected downstream, which is adapted to the second AC voltage provided by the transformer (60) in the outgoing second electrical  To convert DC voltage. 15 18. Power supply system according to claim 16, wherein the  DC-DC converter has a converter topology without galvanic isolation. 19. Energy supply system according to claim 18, in which as  DC-DC converter a converter from the group consisting of: Buck converter, 20 Boost Converter, Buck Boost Converter, Boost Buck Converter is. A power supply system as claimed in any of claims 16 to 19, wherein the double neutral point tap is connected to each of the first and second terminals via the respective direct or indirect connection of the first neutral point (66, 67) and the second neutral point (66, 67) 25 electrical energy storage of the respective nearest to the first neutral point and the second neutral point of the Multilevelkonverters (45, 75) individual modules (48a, 50a, 52a) of the Multilevelkonverters (45, 75) is to be realized. 21. Energy supply system according to one of claims 16 to 20, which is to be arranged in a motor vehicle. 22. Energy supply system according to one of claims 16 to 21, wherein the first sub-network (42, 72) is to be associated as a consumer electrical machine (58) having a plurality of phases, wherein the IVIultilevelkonverter (45, 75) is adapted to each Phase each provide an AC voltage.